The invention relates to an optical sight with a light tunnel, a light emitting diode mounted in the light tunnel for producing an illuminated aimpoint visible in the light tunnel, and an element sensitive to the ambient light for controlling the brightness of the aimpoint in dependence of the intensity of the ambient light, the brightness being reduced in a dark environment so that the shooter does not get dazzled by the illuminated aimpoint, and increased in a bright environment so that the aimpoint will be seen better against the bright background.
A sight of this kind is disclosed in SE-B-449 262. The sight includes an oscillator producing a pulsed current to operate the light emitting diode, and a photoresistor sensitive to the ambient light for controlling the oscillator frequency and pulse length in dependence of the ambient light. It is not indicated where this photoresistor shall be located.
A sight of the kind referred to above is characterized in that the element sensitive to the ambient light, the light sensor, is placed in the light tunnel. This element will thereby detect the ambient light exactly in the area that the shooter aims at when he looks through the light tunnel and places the illuminated aimpoint visible therein, on the designated target. A more adequate control of the brightness of the aimpoint in relation to the ambient light is obtained when the field of view of the light sensitive element is limited to the target area and integrates the light therein. To place a photoresistor in the light tunnel is out of the question since the dimensions of a photoresistor are large, of the order of 5 mm, and the photoresistor hence would interfere with the view through the light tunnel, whereas a photo diode is well suited for this placement since the dimensions of the photo diode are of the order of 0.2 mm, and the photo diode therefore will not cause any such interference. In addition to control of the brightness of the aimpoint being improved by the sight according to the invention this sight is advantageous in that it consumes less power than the known sight with a pulsed light source.
A sight with a light emitting diode is disclosed in U.S. Pat. No. 4,665,622, and a power supply circuit for controlling emission of a light emitting diode is disclosed in U.S. Pat. No. 4,330,206.
Preferably, the light sensitive element is arranged in the close vicinity of the light emitting diode.